Regardless of foreign policy experience, domestic policy agendas, or any outstanding scandals or political gaffes,
this single issue should be at the top of everyone's list when comparing the presidential candidates.
The fact that Trump has repeatedly denied the reality of climate change, even going so far as to claim it was fabricated by China, should be enough to disqualify him from earning your vote.
To put it another (more expansive) way, it is our responsibility as voters to automatically reject any candidate for public office who holds such a belief.
Edit: Credit to u/BenIncognito where credit is due: https://www.reddit.com/r/changemyview/comments/5apx4k/cmv_donald_trumps_belief_that_global_climate/d9icu84/